A special Polish parliamentary commission has opened an investigation into one of the country's biggest financial scams, operated in 2009-2012, with plans to question state authorities of the time.

Observers say European Council President Donald Tusk, who was Poland's prime minister then, could be asked to testify. The commission is led by members of the ruling conservative party, rival to Tusk's party.

On Wednesday, the commission held its first session into the "Amber Gold" pyramid scheme, which deprived some 19,000 people of savings worth some 850 million zlotys ($219 million). The married couple who ran the scheme, identified only as Marcin P. and Katarzyna P., are on trial.

Commission head Malgorzata Wasserman says the aim is to determine why government and finance authorities failed to warn citizens against the scheme.